Twenty-one RCTs with 3,984 participants (2,446 in ondansetron groups and 1,538 in placebo groups; 1,163 PH-PONV+ participants and 2,821 PH-PONV- participants).
The incidence of vomiting in the first 24 hours post-operatively for the patients in the placebo groups was 67.7% in the PH-PONV+ sub-group and 46.4% for patients in the PH-PONV- sub-group, chi- square = 55.64, p < 0.001).
The overall efficacy of ondansetron for the 4 mg dose was OR 2.53, (95% CI: 2.15, 2.97) and OR 2.98, (95% CI: 2.30, 3.87) for the 8 mg dose.
In the sub-groups, the effectiveness of the 4 mg dose of ondansetron was OR 2.40, (95% CI: 1.77, 3.26) for the PH-PONV+ group versus OR 2.71, (95% CI: 2.23, 3.30) for the PH-PONV- group, p = 0.505).
In the sub-groups, the effectiveness of the 8 mg dose of ondansetron was OR 4.21, (95% CI: 2.66, 6.66) for the PH-PONV+ group versus OR 2.61, (95% CI: 1.89, 3.59) for the PH-PONV- group, (p = 0.087).
The global values of NNT calculated for ondansetron 4 mg for the groups with and without PH-PONV were 7.09, (95% CI: 4.83, 13.51) and 5.91, (95% CI: 4.78, 7.69), while for the 8 mg dose they were 2.08, (95% CI: 2.25, 3.77) and 4.11, (95% CI: 3.22, 5.74), respectively.
Nine studies for 4 mg found no statistical difference between groups, and 3 studies of 8 mg found statistically significant differences between groups only in the studies sponsored by the manufacturer.